Conventionally, pneumatic tires with an object of securing straight-line stability are known. For example, the pneumatic tire of Japanese Unexamined Patent Application Publication No. 2002-29216 comprises land portions defined by grooves that intersect a tread width direction cross section in the tread portion. When viewed in the tread width direction cross section, the ground contact surface of the land portions is curved so as to protrude to the outer side in the radial direction, and the apex of the ground contact surface closest to the profile line of the tread surface across the entire tread width is offset from the lateral center of the land portion toward one side edge of the land portion by from 0.1 to 0.4 times the width of the land portion.
Also, Japanese Unexamined Patent Application Publication No. 2004-122904, for example, describes a pneumatic tire comprising a tread surface being defined by circumferential grooves into a center land portion extending along the tire equator, an outer land portion extending in the shoulder portion, an intermediate land portion located between the center land portion and the outer land portion. In the pneumatic tire when in a regular state of being assembled on a regular rim, inflated to a regular internal pressure, and having no load applied, when viewed in the tire meridian cross section including the tire axis, the radius of curvature R1 of the outer surface of the center land portion is greater than the radius of curvature R2 of the outer surface of the intermediate land portion, and the center of each radius of curvature R1, R2 lies is at the same position.
Also conventionally, for example in Japanese Unexamined Patent Application Publication No. 2012-116410 describes a pneumatic tire comprising the tread portion being defined into a plurality of land portions extending in the tire circumferential direction by a plurality of longitudinal grooves extending in the tire circumferential direction. In the pneumatic tire, in a meridian cross section that includes the tire axis, the ground contact surface of each land portion includes a center circular arc surface that passes through the center thereof in the tire axial direction and is formed from a single circular arc that protrudes to the outside in the tire radial direction, and an outside circular arc surface connected to the center circular arc surface on at least one side in the tire axial direction formed from a circular arc having a radius of curvature 30 to 50% the radius of curvature of the center circular arc surface. Also, the amount of camber, which is the distance in the tire radial direction between the outer edge in the tire axial direction of the outside circular arc surface and an imaginary line extending the center circular arc surface to the outer edge side of the outside circular arc surface, is 0.5 to 1.5% of the width of the land portion in the tire axial direction.
Also, for example in Japanese Unexamined Patent Application Publication No. 2011-57141 describes a pneumatic tire with a tread pattern that includes land portions sandwiched between grooves in the tire circumferential direction. In the pneumatic tire, the groove area ratios of the tread pattern in the regions on the two sides in the tire width direction sandwiching the tire equator line are different. The land portions have a shape that protrudes to the outside in the tire radial direction. The land portions include land portion edge portions formed by the groove walls of the tire circumferential direction grooves that sandwich the land portions and the surface of the land portions, and that are in contact with the tire circumferential direction grooves. Of the two sides in the tire width direction sandwiching the tire equator line, the side where the groove area ratio is comparatively large is referred to as the first side, and the side where the groove area ratio is relatively small is referred to as the second side. In the land portions, the amount that the position of a first edge portion that is facing towards the first side is depressed in the tire radial direction from the maximum outer diameter position of the land portion is larger compared with the amount that the position of the second edge portion that is facing towards the second side is depressed in the tire radial direction from the maximum outer diameter position of the land portion.
In recent years, in line with improvements in vehicle performance, pneumatic tires that can achieve both steering stability at high speeds and durability at high speeds with a camber have been demanded. To cater to such a demand to ensure steering stability, a pneumatic tire such as that described in Japanese Unexamined Patent Application Publication No. 2002-29216 has been effective. The pneumatic tire of Japanese Unexamined Patent Application Publication No. 2002-29216 a configuration in which a rib (land portion), formed in the tread portion, has a profile that, when viewed in the tire meridian cross section, protrudes to the outer side in the tire radial direction beyond the profile of the tread surface so that the rib has better contact with the ground. However, with a camber to a vehicle, durability at high speeds tends to decrease, in the case of a negative camber. This is because ribs located on the inner side of the tire equator plane when the tire is mounted to a vehicle have a greater footprint length than ribs located on the outer side of the tire equatorial plane. Consequently, achieving both steering stability at high speeds and durability at high speeds with a camber has been difficult. In Japanese Unexamined Patent Application Publication Nos. 2011-57141 and 2012-116410 also, achieving both steering stability at high speeds and durability at high speeds with a camber has been difficult.
Also, the pneumatic tire described in Japanese Unexamined Patent Application Publication No. 2004-122904 is designed for enhanced durability. However, the pneumatic tire is for light trucks. Also, the pneumatic tire has a configuration in which, due to differences in the radius of curvature, the center land portion protrudes to the outer side in the tire radial direction a great deal more than the intermediate land portion. Consequently, in the case of the pneumatic tire being applied to a vehicle with a camber, durability of the center land portion decreases and steering stability also decreases.